The invention relates to a method for supplying energy to and discharging energy from a resistive-inductive load or a pure inductance.
Applications for the excitation windings can be found in medical appliances or else in synchronous machines, for example. By supplying energy to and discharging energy from the excitation winding, the excitation current is raised or lowered and hence the strength of the magnetic field influenced.
Often, such excitation windings are also made from HTS (High Temperature Superconductor) materials which need to be kept at a temperature of <80 K in order to maintain superconductivity. To maintain this low temperature, supply of heat from the outside and generation of heat in the cooled area need to be largely avoided.
The electrical power required for excitation and de-excitation is often very high because the process of excitation and de-excitation needs to take place very quickly in order to achieve a high control quality. To avoid high losses when supplying and discharging electrical power in order to alter the current through the inductive load, it is advantageously possible to use a relatively high voltage and to perform voltage transformation directly before the inductive load is fed.
To feed the excitation winding directly from the outside, the high current levels in the region of up to a few 100 A mean that it is necessary to use lines having an appropriate cross section which are therefore also good conductors of heat. Instead, it is better for the balance of thermal power loss if relatively high voltages are used for the supply of energy from the hot to the cold area and hence the conductor cross section is reduced. The voltage then likewise needs to be transformed by a transformer in the cold area and rectified in order to feed the excitation winding.
Specifically in the case of applications for superconductive excitation windings in which the energy is transferred from the ambient temperature (what is known as the “hot area”) to a temperature which allows superconduction (what is known as the “cold area”), this results in reduced losses in the bushings from the hot to the cold area.